1. Field of the Invention
This invention relates generally to a method and apparatus for data transfer using FSK signals and in particular to peer to peer data communication using pre-existing caller ID CLASS FSK signaling infrastructure.
2. Background
Introduction of SS7 switching in central office switching systems provided the technological capability to introduce caller ID services to customers. Caller ID services utilize the ability of a modern call switching and routing system, referred to in the telecommunications industry as a Stored Program Control System (SPCS), to record and provide to a call recipient information regarding the calling party in a Calling Party Number Message (CPN Message). This information, commonly referred to as caller ID information, may comprise the calling party's telephone number or name.
Telephones capable of displaying caller ID information are increasingly common. In fact, caller ID services are one of a group of network-provided enhanced services known as custom local area signaling services (CLASS). Telecordia Technologies, Inc., Morristown, N.J., originally Bellcore, has defined three classes of caller ID services, known respectively as Type I, Type II, and Type III. In the Type I service, a phone is equipped with a Frequency Shift Key (FSK) detector, a controller, and a display. When a call is placed to the phone, a SPCS server situated within the Public Switched Telephone Network (PSTN) activates a corresponding FSK generator also situated within the PSTN to transmit to the phone a FSK signal encoding the caller ID information. At the phone, as indicated in FIG. 1, when a first ring is detected, step 100, the controller enables the FSK detector, step 102, which listens for a FSK signal. If a FSK signal is detected before the second ring, the Yes branch of decision point 104, it is demodulated to obtain the caller ID information. That information is then displayed, step 106. If, however, the FSK signal is not detected before the second ring, the No branch of decision point 104, the FSK detector is disabled, step 110.
In the Type II or Type III service, a phone is also equipped with a Customer Premises Equipment Alerting Signal (CAS) detector. When a call is placed to the phone, as illustrated in FIG. 5, the SPCS server first determines if the phone is on-hook or off-hook. If on-hook, the procedure described for the Type I category of service is followed. If off-hook, step 250, a call waiting/caller ID service is provided in which the server first activates a corresponding CAS generator situated within the PSTN to generate and transmit a CAS signal to the phone, step 252. The CAS detector at the phone, which has been previously enabled by the controller upon the occurrence of the off-hook condition, listens for the CAS signal, indicated by the No loopback to the beginning of decision point 254. Upon detecting the CAS signal, indicated by the Yes branch of decision point 254, the controller mutes the audio channel at the phone, step 256, and sends a Dual Tone Multi-Frequency (DTMF) tone, which serves as an acknowledgement signal. In the case of a Type II unit, the acknowledgement signal is a DTMF `D` tone; in the case of a Type III unit, the acknowledgement signal is a DTMF `A` tone. Muting of the audio channel is required since the FSK signal in one implementation is transmitted at a range of frequencies, 500-2500 Hz, which is within the audio band of 0 to about 3000 Hz.
The controller then enables the FSK detector, step 258, which listens for an FSK signal. If a FSK signal is detected before a predetermined timeout period, indicated by the Yes branch of decision point 260, the FSK signal is demodulated and the caller ID information obtained and displayed, step 262. If there is a timeout before the FSK signal is detected, indicated by the No branch of decision point 260, the controller un-mutes the audio channel, step 264, and resumes listening for a CAS signal, indicated by the branch from block 264 to the beginning of decision point 254.
As indicated, the process for the Type III service is identical to that of the Type II category, except that the acknowledgement signal is a DTMF `A` tone. This identifies the Customer Premises Equipment (CPE), that is, the phone, as a Type III unit.
An Analog Display Services Interface (ADSI) is a Telecordia-defined interface and related protocol for bi-directional transmission of data between a SPCS server and an ADSI-compatible phone. The interface is such that an ADSI-compatible phone is backward compatible with a Type III phone. Data transmission to the phone is achieved via the FSK receiver already present in the phone. In early embodiments, data transmission from the phone was achieved by DTMF tones. In later embodiments, a FSK generator was added to a Type III phone, and data transmission from the phone originated from the FSK generator.
The class of services which can be supported through the ADSI is limited to those services which involve communication between a SPCS server and an ADSI-compatible phone, such as the transmission or reception of e-mail messages. However, services involving peer-to-peer communication, that is, direct communication between two CPEs, is not supported by the ADSI even though such services are desirable and unmet by the services supported by the ADSI interface.
Furthermore, it would be desirable to offer such services using the existing infrastructure for caller ID and ADSI services to the extent possible.
Therefore, a need exists for a data communication mechanism that allows peer-to-peer transmission of data over a telecommunications network using the existing infrastructure for CLASS Caller ID FSK signals.